EP0759848A1

EP0759848A1 - Device and process for producing a three-dimensional object by laser sintering

Info

Publication number: EP0759848A1
Application number: EP96907426A
Authority: EP
Inventors: Christian Wilkening; Thomas Mattes
Original assignee: EOS GmbH
Current assignee: EOS GmbH
Priority date: 1995-03-20
Filing date: 1996-03-11
Publication date: 1997-03-05
Anticipated expiration: 2016-03-11
Also published as: WO1996029192A1; EP0759848B1; JPH09506553A

Abstract

The object is a device for producing a three-dimensional object by the successive solidification of layers of a material hardenable by electromagnetic or particle radiation at the points corresponding to the cross-section of the object. The component is to be produced in a short time and with greater precision than before. To this end the device has a support (9) adjustable for height, a device for applying (12) a layer of the hardenable material (13) to the support (9) on a previously formed layer and an irradiation device (4) and a control (8) for the irradiation device for irradiating points of the layer corresponding to the object (3). There is a heating device to solidify a region of the material (13) surrounding the object (3) by the effect of heat.

Description

Device and method for producing a three-dimensional object by means of laser sintering

The invention relates to a device and a method for producing a three-dimensional object by means of laser sintering according to the preamble of claims 1, 5 and 9.

Such a device is known from DE 43 00 478 C1. As can be seen from FIG. 1, the known device has a substantially horizontally arranged work table 1 with a hole in the form of a cutout 2. The cutout 2 is larger than the largest cross-sectional area of an object 3 to be produced. Above the work table 1 there is an irradiation device 4 in the form of a laser, which emits a directed light beam 5. This is directed via a deflection device 6 as a deflected beam 7 onto the level of the work table 1 distracted. A controller 8 controls the deflection device in such a way that the deflected beam 7 strikes any desired location within the work area defined by the cutout 2.

Below the cutout 2 is also a substantially horizontally arranged base 9 in the form of a platform is provided, which by means of a height adjustment device 10 in the direction of arrow 11 between a highest position in which the surface of the base 9 within the cutout 2 and essentially in the same Height as the surface of the work table 1, and a lowest position in which the distance between the base and the work table is greater than the maximum height of the object 3, is displaceable.

A device 12 for applying a uniform layer of a powdery material 13 which can be solidified by the action of electromagnetic radiation, which is designed, for example, as a storage container with a wiper for smoothing the layer, can be moved horizontally over the work table 1 via the cutout 2.

The controller 8 and the height adjustment device 10 are each connected to a central control unit 14 for coordinated control of these devices.

The operation of such a device for producing a three-dimensional object is known under the name of laser sintering.

In operation, in a first step, the base 9 is moved to the highest position by means of the height adjustment device 10, in which the surface of the base 9 lies in one plane with the surface of the work table 1 and then by the amount of the intended thickness of the first material layer lowered, so that a recessed area is formed within the cutout 2, which is laterally from the Walls of the cutout 2 and below is limited by the surface of the base 9. Then a first layer of the material 13 is applied and smoothed by means of the device 12 with the intended layer thickness in the cavity formed by the cutout 2 and the base 9. The control unit 14 then controls the deflection device 6 via its control in such a way that the deflected light beam 7 strikes those parts of the layer which are to be solidified in accordance with coordinates of the object 3 stored in the control unit 14 and where the material sinters there. The control unit 14 is then controlled in such a way that the deflected light beam strikes only the region of the material layer adjoining the inner surface of the cutout 2 and the material layer is solidified there by sintering, as a result of which a first annular wall layer is formed, which contains the remaining powdery material of the layer completely surrounds.

It is also possible to completely solidify the first layer of the material applied to the base 9 by the laser beam, so that a firm bottom layer is formed.

In further steps, the base 9 is lowered by the amount of the layer thickness of the next layer, and then proceed as in the first step. Characterized in that an annular wall layer is sintered onto the underlying annular wall layer in the production of each object layer, an annular wall region 15 is formed in the form of a container wall, which encloses the object 3 together with the remaining non-sintered material 13 and thus when lowering the base 9 under the work table 1 prevents leakage of the material 13. The steps are repeated until the object 3 is completed.

The co-solidified container wall 15 holds unsolidified powder 13 in place. The unconsolidated powder thus acts as a support for layers above. In addition to the cylindrical container wall 15, a bottom and a Solidified lid, so long cooling times for the object formed in the laser sintering system can be avoided, since the object with its container can be completely removed from the system and brought to a separate location for cooling.

However, the known method has the following disadvantages. The container wall 15 represents a separate component which has to be irradiated layer by layer. This makes the construction time unnecessarily long. The focus of the laser beam usually deteriorates at the edge, that is to say in the area in which the container wall is to be solidified. The safe construction of a stable container wall is therefore difficult.

A further disadvantage is that the container wall generated with the laser is also solidified when each layer of the object is solidified, so that it represents an obstacle for the wiper 12, which strokes the surface of the layer with a certain pressure, whereby it can be damaged with each new coating process.

In the event that the first layer on the base 9 as the bottom layer is completely solidified by the laser beam, the production requires. the completely solidified bottom layer by the laser, however, a lot of time.

Furthermore, the following problem arises in the laser sintering process described above without complete solidification of the first layer applied to the base. The base, which usually consists of a metal platform, must be adjusted exactly parallel to the plane of movement of the scraper so that the powder layers have a uniform thickness over the entire surface. In practice, this adjustment is not possible with sufficient accuracy, especially with small layer thicknesses. Furthermore, the known method cannot be carried out using synthetic resin-coated molding sand as the material to be solidified, since when irradiated with the laser beam no thin but sufficiently stable container wall can be produced.

The object of the invention is to provide a device for producing a three-dimensional object, with which the component can be produced in a short time and with greater accuracy than hitherto.

The object is achieved by the device according to patent claim 1, 5 or 9.

Further training is given in the subclaims.

The device has the advantage that there is no irradiation time for the container wall or the frame. This saves a lot of time. In particular, the device is suitable for the use of molding sand as the material to be consolidated.

Furthermore, the device has the advantage that it enables the production of a bottom layer with a surface lying exactly parallel to the scraper plane within a short time. The floor layer created in this way can serve as a foundation for anchoring the object.

Further features and expediencies result from the description of exemplary embodiments with reference to the figures.

From the figures show:

1 shows a schematic cross-sectional view of a known device for producing a three-dimensional object by means of laser sintering; 2 shows a schematic cross-sectional view of an embodiment of the device according to the invention for carrying out the method;

3 shows a schematic cross-sectional view of an embodiment of a heatable base;

FIG. 4 is a plan view in the direction of arrow A on the heatable base of FIG. 3 along the section line I - I of FIG. 3; and

Fig. 5 is a cross-sectional view of a further embodiment of the work table with heating device.

As can be seen from FIG. 2, the device according to the invention has the same components as the device shown in FIG. 1. Therefore, the description of components with the same reference numerals is not repeated here.

In addition, the device has a heating ring 16, for example in the form of a heating spiral, which is arranged in a recess 17 in a wall 18 of the work table 1 delimiting the cutout 2. The heating coil 16 is fitted into the recess 17 in such a way that it closes positively with the wall 18. The recess 17 on the work table 1 is not located directly on the work surface, which is defined by the point of impact of the laser beam 7 on the surface of the material 13, but a few centimeters below the work surface. The support 9 can be heated in the device, so that the first layers of the material 13 applied to the support 9 can be solidified by the action of heat.

In operation, as in the known device, the base 9 is first moved into the highest position by means of the height adjusting device 10, in which the surface of the Surface 9 lies in one plane with the surface of the work table 1, and then lowered by the amount of the intended thickness of the first material layer, so that a recessed area is formed within the cutout 2, which is laterally from the wall 18 of the cutout 2 and below is limited by the surface of the base 9. By means of the application device 12 a first layer of powdery, sinterable material 13, for example molding sand, which consists of quartz sand with a phenolic resin coating, is then provided with the intended layer thickness in the lowered area formed by the cutout 2 and the base 9 brought in.

Then, in contrast to the prior art, the base 9 is heated in such a way that the first layer thus applied is solidified by the action of heat (sintered and thus). In this way, a firm bottom layer 20 is first formed. The required temperature for solidification is between 80 ° C and 160 ° C depending on the material.

In a second step, the base 9 is lowered by the control unit 14 by the amount of at least one layer thickness by means of the height adjustment device 10 and a quantity of the molding sand 13 corresponding to at least one layer thickness is introduced and smoothed into the resulting reduced area within the cutout 2 by means of the application device 12 . There is thus at least one layer of unconsolidated material 13 above the consolidated soil layer 20.

After lowering the base by the amount of the layer thickness of the next layer, applying and smoothing the material 13, the production of the object 3 itself can now begin. For this purpose, the control unit 14 controls the deflection device 6 in such a way that the deflected light beam 7 strikes those points of the layer which are to be solidified in accordance with the coordinates of the object 3 stored in the control unit 14. As soon as the undersolidified material 13 surrounding the object 3 reaches the area of the heating coil 16 by lowering the base 9, an annular region of the material 13 surrounding the object 3 and the still unconsolidated material 13 is solidified by the action of heat via heat conduction. The annular area has a vertical extension of several layer thicknesses, corresponding to the vertical extension of the recess 17 or the heating spiral 16. Since the base 9 before the solidification of a new layer of the object 3 each by a layer thickness, for example in the Is a range of a few tenths of a millimeter, is lowered, there are several layers for a longer period of time in the area of influence of the heat of the heating coil 16. Thus, the container edge 15 is continuously made of overlapping annular areas of the wall 18 of the Aus¬ cut 2 adjacent molding sand 13 solidified. The time in which the molding sand remains in the area of action of the heating coil 16 is between 20 minutes and one hour, depending on the construction speed. Depending on this, the heating coil has a temperature of 80 ° C to 160 ° C. The faster the building process takes place, ie the shorter the material 13 is in the heating area, the higher the temperature must be selected.

Molding sand is particularly suitable as a material because there is no bonding between the molding sand and the heating coil.

The container wall thus formed prevents the material 13 from escaping when the support 9 is lowered under the work table 1, due to the fact that the container wall 15 does not extend to the work surface, as is the case with the conventional solidification of the container wall by means of laser exposure the container wall is not an obstacle for the wiper of the application device 12 during a new coating process. Since the heat effect on the one to be solidified If the edge region is separated from the irradiation of the layers, the irradiation time necessary in the known method can be saved. The time saved is about 20 s per shift.

After completion of the last object layer, the container wall 15 is further solidified with the steps described above, so that it projects over the object 3 by a few layer thicknesses and then a cover layer 21 is solidified by means of radiation with the laser 4, which together with the bottom layer 20 and the container wall 15 forms a container tightly enclosing the object 3 and the remaining unsintered material 13.

The container with the object 3 contained therein can then be removed from the base 9 and brought to a separate location for cooling, so that the production of a new object can immediately begin again.

Modifications are possible. The production of the bottom layer 20 and / or the cover layer 21 can thus be dispensed with. This is particularly suitable when the object is to cool down in the system and reliable cooling - also of the residual powder then exposed - is possible in the container 15. Alternatively, the bottom layer 20 can also be solidified by irradiation with the laser. The application device 12 can also be designed as a roller, as a slide or as a broom or in any manner suitable for applying a uniform layer of powdery material. The cross section of the cutout 2 does not necessarily have to be circular, it can also be square or rectangular or have any shape. Instead of using a heating coil, it is also possible to heat the work table over the entire thickness or to use a heating lamp. Furthermore, a cover layer can also be solidified by the action of heat by placing a heatable cover on the container wall or by irradiating the uppermost unconsolidated layer with a heat lamp. The device is not only suitable for the use of molding sand, but also plastic-coated ceramic or metal powder can be used. It is also possible to use a light-curable polymer as the material to be solidified. Furthermore, any other radiation source for electromagnetic radiation which emits a directed light beam with sufficient energy for sintering, such as, for example, a UV lamp, can be used as the radiation device. Irradiation by means of electron beams from an electron beam source is also conceivable.

In a further exemplary embodiment, the container wall 15 is solidified by means of a liquid adhesive which is fed to the material to be solidified in the edge region adjacent to the work table and there causes its gluing. The liquid adhesive is fed to the material 13 via a tube which is fitted into the recess 17 and has a plurality of outflow nozzles. When using molding sand as the material to be consolidated, an adhesive with a setting time of approximately 20 minutes to one hour is used, depending on the construction time of the object. The adhesive must be selected so that it does not connect to the tube, which is usually made of metal. As an alternative to supplying the liquid adhesive, a binder substance of an adhesive can also be added to the material 13 prior to solidification, which reacts with a hardening substance supplied via the tube and thus solidifies the material.

An embodiment of the heated pad 9 is shown in Figures 3 and 4. For this purpose, the sintering device according to FIG. 2 has a square cutout 200 in its worktable 1. The base 9 is in the form of an essentially square platform 90, the cross section of which is somewhat less than that of the cutout. The platform 90 has a cover plate 91 and a base plate 92, the plates being made of a highly thermally conductive material. rial, especially made of aluminum. The base 9 is arranged in the laser sintering device so that the cover plate 91 faces the object. A heating device for heating the cover plate 91 in the form of a heating wire 93 is provided between the cover plate 91 and the base plate 92. The heating wire 93 is arranged directly under the cover plate 91 and is in contact with it. On its side facing away from the cover plate 91, the heating wire is thermally insulated from the base plate 92 by a heat-insulating plate 94, for example made of Dotherm 500. The heat generated by the heating wire 93 is thus released to the cover plate 91. The heating wire 93 has a diameter of approximately 2 mm and is arranged in the plate plane over the entire cross section of the plate in the form of meandering windings, as can be seen in particular in FIG. 4. The length and the mutual spacing of the turns is determined by a plurality of spacer disks 95 attached to the underside of the cover plate, around which the heating wire is looped. The meandering guidance of the heating wire 93 and the good thermal conductivity of the cover plate 91 ensure that the temperature distribution over the cover plate 91 is almost constant. The heating power of the heating wire is about 840 W.

Between the cover plate 91 and the heat-insulating plate 94, a peripheral sealing lip 97 made of silicone is provided on the edge 96 of the platform. The sealing lip 97 serves to seal the intermediate space between the edge 96 of the platform and the wall delimiting the cutout 200 when the platform 90 for applying and solidifying the first powder layers is still inside the cutout 200 of the work table. The sealing lip 97 thus prevents powder or molding sand from passing through when the first layers are applied.

In operation, when the heated platform 90 is used, a bottom layer made of solidifiable material, in particular from molding sand, the thickness of which is a few layer thicknesses of the object to be produced 3 and preferably about 3 to 5 cm, applied and heated by the heatable platform 90 for about 5 to 10 minutes, solidification occurring. The bottom layer produced in this way serves as the foundation for anchoring the object 3, which is not possible when the object 3 is solidified directly on the metallic platform or on a bottom layer that has only one layer thickness.

5 shows a further embodiment of the heating device according to the invention for solidifying the container wall 15. The work table is designed as a plate 50, the upper side 51 of which faces the laser beam 7 or the application device 12. The plate 50 has in its center a circular cutout 52 through which the height-adjustable base 9 can be displaced in the vertical direction. Adjacent to the underside 53 of the plate facing away from the upper side 51, a heat-insulating plate 54, for example made of Dotherm 1100, is provided with a circular cutout 52a coaxial with the circular cutout 52 of the worktop 50 and having the same diameter as that of the cutout 52. The heat insulating plate 54 is fixed to the underside 53 of the plate 50 via a plurality of screws 55. At the end 56 of the heat-insulating plate facing away from the underside 53 of the plate 50, a heating ring 57 is provided, the inside diameter of which corresponds to the diameter of the circular cutout 52 or 52a. The outer diameter of the heating ring 57 is slightly smaller than the diameter of the heat-insulating plate 54. The heating ring 57 is designed in the form of a copper ring and has an annular recess or groove 58 with a rectangular cross-section on its side facing the underside 56 of the heat-insulating plate 57 on. A heating wire 59 is provided in the annular recess 58. The diameter of the annular recess 58 is somewhat larger than the diameter of the circular cutout 52 vertical direction has a thickness d, which determines the height of the annular wall area to be consolidated by the action of heat when the base 9 is lowered in the circular cutout 52.

A programmable logic controller PLC is provided to control and regulate the heating power of the heating wire.

In operation, this transmits a signal to a computer contained in the central control unit 14 when the coating, ie the application of a new powder layer, is started. The computer measures the time between two signals generated during successive coating processes and uses this to determine the exposure time t _{s of} the layer. Assuming that the exposure time for the subsequent layer will be just as long, the heating power P _H is regulated via the heating current of the heating wire 59 so that the thermal energy introduced into the material by the heating ring ^UA constant number of layers. Since there are in each case a plurality of layers in the area of the heat effect of the heating ring 57, any heat supply that is too large or too small for one layer is compensated for again during the solidification of the next layer. The control of the heating power is thus integrally carried out over a plurality of layers. This causes a container wall with an essentially constant wall thickness to be produced.

Alternatively, the heating power can also be regulated in such a way that when the signal that is generated during a new coating is received, the heating current is set to a fixed value ^I max and is then reduced linearly until the signal for the subsequent coating process is measured. In turn, a regulation of the heating current that is integrated over several layers is achieved via the height of I _maχ and the increase in the linear drop in the heating current during the exposure time.

Claims

PATENT CLAIMS

1. Device for producing a three-dimensional object by successively solidifying layers of a material that can be solidified by means of electromagnetic radiation or particle radiation at the locations corresponding to the respective cross section of the object, with a height-adjustable base (9), a device for applying (12) a layer of the solidifiable material (13) on the base (9) or on a previously formed layer, an irradiation device (4) and a controller for the irradiation device (8) for irradiating the locations corresponding to the object (3) the layer, and a heating device (16) for solidifying an area of the material (13) surrounding the object (3) by the action of heat, whereby a work table (1) with a cutout (2) corresponding to the surrounding area (15) is provided, thereby characterized in that the heating device is arranged below the work table (50) Neten and from this thermally insulated heating ring (57) which has an inner diameter corresponding to the diameter of the cutout (52) of the work table (50) and which is arranged coaxially to the axis of symmetry of the cutout (52).

2. Device according to claim 1, characterized in that the base (9) can be raised to a position in which its surface within the cutout (2) lies essentially in one plane with the surface of the work table (1).

3. Device according to one of claims 1 or 2, gekenn¬ characterized by a controller for controlling and regulating the heating power of the heating device (16, 57) such that the thermal energy introduced into the material via the solidification one each Plurality of successive layers of the object (3) is constant.

4. Device according to one of claims 1 to 3, characterized in that the base (9) comprises a heatable platform.

5. Device for producing a three-dimensional object by successively solidifying layers of a material that can be solidified by means of electromagnetic radiation or particle radiation at the locations corresponding to the respective cross section of the object, with a height-adjustable carrier (9) for carrying the object, a device for Applying a layer of a solidifiable material (13) to the carrier (9) or to a previously formed layer, an irradiation device (4) and a controller for the irradiation device (8) for irradiating the object (3 ) corresponding points of the layer, characterized in that the carrier (9) is designed as a plate (91) and a device (93) for heating the carrier is provided, which has a plate (91) on the underside of the plate facing away from the object (3) ) attached heating wire (93).

6. The device according to claim 5, characterized in that the heating wire (93) in meandering turns on the underside of the plate (91) is attached.

7. The device according to claim 5 or 6, characterized gekennzeich¬ net that a heating device (16, 57) for solidifying an object (3) surrounding area of the material to form a container wall (15) is provided.

8. Device according to one of claims 1 to 7, characterized in that the irradiation device (4) comprises a laser.

9. A method for producing a three-dimensional object, in which the object (3) is produced in layers by applying a layer of material (13) that can be solidified by means of electromagnetic radiation or particle radiation and then irradiating it at the points corresponding to the object (3) is solidified, in order to produce a container wall (15) for the material, an area of the material surrounding the object is also solidified, the area being solidified by the action of heat by means of a heating device, characterized in that the heating power of the heating device is regulated such that the thermal energy introduced into the material during the solidification of a plurality of successive layers of the object (3) is constant.

10. The method according to claim 9, characterized in that a programmable controller is used for controlling and regulating the heating power.

11. The method according to claim 9 or 10, characterized in that a powder material is used as the material.